A method and an apparatus for casting under pressure, using a counterpressure in the mold, are known. Their drawback is the possibility that previous metallurgical processes may be disturbed. This drawback can be eliminated only by prolonging the duration of the casting step, leading to a reduction of productivity. This process is characterized by widely variable pressure conditions of the casting formed by the feeding tube and the mold, which is filled initially with gas at atmospheric pressure; then the pressure is increased to its operating value; the volume is filled with molten metal; the gas is discharged through the venting channels of the mold; and at the end of the process, the pressure is relieved. This volume (casting space) is enclosed between walls which, during the casting process come into contact first with gas and then with the moving level of the melt. The venting channels of the mold have a small size which does not let through molten metal, but only gas with a high degree of throttling. The design of the apparatus has the disadvantage that when gas of the same pressure is applied to the mold chamber and to the reservoir chamber for the molten metal, because of the throttling in the venting channels, the increase of the pressure in the casting space is delayed and molten metal enters it prematurely. If the pressure in the reservoir chamber is maintained to avoid random motion of the melt, there is a danger that gas may enter this reservoir from the mold through the feeding tube.
An improved apparatus for casting under gas pressure using gas counterpressure is known, in which these drawbacks are avoided by providing a controllable connection between the casting space, formed by the mold together with the feeding tube, and the reservoir chamber. This connection is effected by means of a closeable opening (aperture), located on the wall of the casting space. It is a drawback of this system that in the processing of highmelting metals at temperatures over 1000.degree. C, the passage of the metal through a syphon-type feeder tube and its closing between both chambers for multiple casting is impossible.
It is another drawback of this method that, because of the initially produced pressure, the gases from the melt cannot be readily separated (released) during the casting process.
The aforementioned method, as well as other known methods and apparatuses for casting under pressure or with counterpressure are used for aluminum and aluminum alloys, while application of similar techniques for high-melting metals with a melting temperature higher than 1000.degree. C is difficult.
Also known is a method for injection casting, in which the transfer of the molten metal into the mold is carried out under the action of pressure. This casting method has been applied successfully mainly for nonferrous metals and for castings of high weight and simple shape.